This invention relates generally to pilot ejection systems for aircraft, and, more particuarly, to a windblast head protector for use during pilot ejection from the aircraft.
Crew safety is considered to be of utmost importance when designing todays high performance aircraft. This is of special consideration during times of aircraft malfunction which results in the necessity of the pilot "bailing-out" of the aircraft. Consequently, many advances have been made in pilot ejection methods and systems.
The ACES-II ejection seat manufactured by McDonnell Douglas Corporation is currently utilized in a majority of high performance aircraft such as the F-16, F-15 and A-10. Unfortunately, high speed ejection can cause a variety of injuries to the ejecting crew member. Head and/or neck injury to a crew member can occur as a result of conditions set forth hereinbelow which arise while the crew member ejects from the aircraft in an open ejection seat at high dynamic pressures.
First, aerodynamic flow over the top of the standard helmet causes a large pressure drop to occur so that the normal pressure inside the helmet acts to push the helmet away from the head with 400 or more pounds force. If the helmet is retained on the head of a crew member, these loads must then be born by the chin strap and jaw. If the helmet is lost, the soft tissues of the face are likely to be damaged by the windblast or head injury may occur at ground landing.
Second, during the first few hundred milliseconds after ejection, before the decelerator/stabilizer drogue parachute inflates, the mass of the seat combined with that of the crewman's torso cause them to have a lower drag/mass than the head. This situation can cause a flailing of the head to take place in the windblast. In the absence of aerodynamic unstability in the seat and/or helmet and O.sub.2 mask assembly, the headrest would normally support the head/helmet against net windblast loads. However, both the ejection seat and the helmet/mask are aerodynamically unstable so that the headrest is ineffective in providing the needed support to the head and neck. A larger headrest could be provided but this would greatly reduce the pilot's external vision and, thereby, reduce the overall effectiveness of the aircraft. The helmet could be restrained to the headrest by a retractable cord but the large relative displacement between seat and crewman at drogue inflation would result in dangerous loads in the neck.
Third, a combination of roll instability and pitch moments due to the main chute motor and drogue release delay cause a tendency of the seat to turn its side to the inflating main parachute. The pitch-up roll maneuver leading to this has a high probability of causing the distol parachute rise and therefore move between the headrest and helmet so that opening shock loads may be directly born by the neck. The restraint release delay could be increased but this would only partially reduce the shear loading of the neck while reducing the safety margin on the main chute load capacity.
As is readily apparent from the above-identified problems encountered by crewman during ejection and the unsucessful attempts to solve these problems, it becomes essential to provide additional safety equipment on existing ejection seat equipment. This safety equipment must not only be capable of increasing crew member safety, but it must also prevent any decrease in aircraft performance during periods of nonuse.